1. Field of the Invention
The present invention relate to an advanced method for the preparation of pyrido benzoxazine derivatives and pharmaceutically acceptable salts, antibacterially active compounds and, more particularly, to an improvement in production cost and production yield along with the novel method.
2. Description of the Prior Art
According to literature (Chem. Pharm. Bull., 32, pp 4907-4913 (1984)), it is reported that the pyrido benzoxazine derivatives which are represented by the following general formula I are very antibacterially active compounds and have potent sterilization power for a wide range of bacteria: ##STR2## wherein X is a fluorine atom or chlorine atom and R is an alkyl group containing 1 to 4 carbon atoms.
Preparation methods for the antibacterially active compound of the formula I are disclosed in many patents, for example, Korean Patent Publication No. 84-2141 and Korean Patent Laid-Open Publication Nos. 92-22050, 93-4309, 93-4310, 93-10027, 93-10041 and 93-12787.
Those conventional methods, however, are disadvantageous in many aspects. For example, the reaction procedure employed in the conventional methods is carried out in even 8 steps using 2,3,4-trifluoronitrobenzene as a starting material, so that production yield is low. Further, since the conventional methods use Raney Nickel, which is dangerous due to strong flammability, it is unsuitable to industrial mass production.